In general, in order to detect light, for example detection of natural light or artificial light, detection of interruption of continuous incident light, and detection of frequency of pulsed light, light detection components and power supplies in addition to peripheral electronic circuits must be provided to light detection systems. In such cases, the light detection components and the power supplies are usually prepared as separated units. Porous silicon is known as a light-emitting element or a light-emitting and receiving element (for example, see Patent Document 1). A photodetector using direct-transition-type porous silicon is also known (for example, see Patent Document 2).
Patent Document 1: Japanese Unexamined Patent Application Publication No. 4-356977 (Japanese Patent No. 3306077)
Patent Document 2: Japanese Unexamined Patent Application Publication No. 5-37000 (Japanese Patent No. 3216153)